Whole-body magnetic resonance imaging (WBMRI) has emerged as a useful imaging tool in diagnosing and characterizing the progression of myopathies and muscular dystrophies. WBMRI indications and diagnostic efficacy are becoming better defined with the increasing number of cases, publications and discussions within multidisciplinary working groups. Advanced WBMRI protocols are rapid, lower cost, and well-tolerated by patients. Accurate interpretation of muscle WBMRI requires a detailed knowledge of muscle anatomy and differential pattern of involvement in muscle diseases. With the surge in recently identified novel genetic myopathies, WBMRI will become increasingly useful for phenotypic validation of genetic variants of unknown significance. In addition, WBMRI will be progressively used as a biomarker for disease progression and quantify response to therapy with the emergence of novel disease modifying treatments. This review outlines WBMRI indications and updates refined protocols and provides a comprehensive overview of the diagnostic utility and suggested methodology of WBMRI for pediatric and adult patients with muscle diseases.